The controversial letter signed by 47 Republicans to Iran's leaders authored by Sen. Tom Cotton should yield a better agreement if used properly by the Obama administration, Sen. Rob Portman said Thursday.

Portman, who faces a re-election fight next year in Ohio, said he didn't see the letter as a way to sabotage the talks — quite the opposite.

“I signed it for a very simple reason, which is I want a good agreement with Iran, and I think it helps to get a good agreement," Portman told reporters.

"As you all know, because you cover us up here, it’s the Congress that has taken the lead on sanctions, it’s the Congress that insisted on sanctions, it’s the administration that was reluctant, it was sanctions that got Iran to the table in the first place," he said.

"And the letter states the obvious, which is Congress is going to have a role here, but it also reminds those negotiators at the table, on the other side of the table from us, that this has to be a verifiable, strong agreement that actually ends their nuclear weapons program. And if it is not, well it’s not going to pass muster here. And I think that helps to get a good agreement."

Portman, who has experience in international negotiations as a former U.S. trade representative, said he hopes the administrations uses the leverage of Congress "to let the Iranians know that this has got to be real. And if it’s not, it’s not going to withstand the test of time. And I’m hopeful that we’ll see, out of this whole process, a stronger agreement and one that we can all support.”